Various "reserved" areas of FB (frame buffer: vidmem) have to be
calculated, because the GSP booting process needs this information.

PMU_RESERVED_SIZE is computed at compile time using const_align_up() and
applied only for Blackwell dGPU architectures. All other architectures
leave it at zero, matching Open RM behavior.

Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 drivers/gpu/nova-core/fb.rs     | 38 ++++++++++++++++++++++++++++++---
 drivers/gpu/nova-core/gsp/fw.rs |  1 +
 2 files changed, 36 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/nova-core/fb.rs b/drivers/gpu/nova-core/fb.rs
index 35899e9b2560..c2005e4b4177 100644
--- a/drivers/gpu/nova-core/fb.rs
+++ b/drivers/gpu/nova-core/fb.rs
@@ -12,6 +12,7 @@
     io::Io,
     prelude::*,
     ptr::{
+        const_align_up,
         Alignable,
         Alignment, //
     },
@@ -22,10 +23,16 @@
 use crate::{
     driver::Bar0,
     firmware::gsp::GspFirmware,
-    gpu::Chipset,
+    gpu::{
+        Architecture,
+        Chipset, //
+    },
     gsp,
-    num::FromSafeCast,
-    regs, //
+    num::{
+        usize_into_u32,
+        FromSafeCast, //
+    },
+    regs,
 };
 
 mod hal;
@@ -168,6 +175,8 @@ pub(crate) struct FbLayout {
     pub(crate) wpr2: FbRange,
     pub(crate) heap: FbRange,
     pub(crate) vf_partition_count: u8,
+    /// PMU reserved memory size, in bytes.
+    pub(crate) pmu_reserved_size: u32,
 }
 
 impl FbLayout {
@@ -268,6 +277,29 @@ pub(crate) fn new(chipset: Chipset, bar: &Bar0, gsp_fw: &GspFirmware) -> Result<
             wpr2,
             heap,
             vf_partition_count: 0,
+            pmu_reserved_size: match chipset.arch() {
+                Architecture::BlackwellGB10x | Architecture::BlackwellGB20x => PMU_RESERVED_SIZE,
+                _ => 0,
+            },
         })
     }
 }
+
+/// Returns the PMU reserved memory size for `chipset`.
+#[expect(dead_code)]
+pub(crate) fn calc_pmu_reserved_size(chipset: Chipset) -> u32 {
+    match chipset.arch() {
+        Architecture::BlackwellGB10x | Architecture::BlackwellGB20x => PMU_RESERVED_SIZE,
+        _ => 0,
+    }
+}
+
+/// PMU reserved size, aligned to 128KB.
+pub(crate) const PMU_RESERVED_SIZE: u32 = usize_into_u32::<
+    {
+        match const_align_up(SZ_8M + SZ_16M + SZ_4K, Alignment::new::<SZ_128K>()) {
+            Some(v) => v,
+            None => panic!("PMU_RESERVED_SIZE: alignment overflow"),
+        }
+    },
+>();
diff --git a/drivers/gpu/nova-core/gsp/fw.rs b/drivers/gpu/nova-core/gsp/fw.rs
index 3245793bbe42..5d36604ea1a3 100644
--- a/drivers/gpu/nova-core/gsp/fw.rs
+++ b/drivers/gpu/nova-core/gsp/fw.rs
@@ -247,6 +247,7 @@ pub(crate) fn new<'a>(
             fbSize: fb_layout.fb.end - fb_layout.fb.start,
             vgaWorkspaceOffset: fb_layout.vga_workspace.start,
             vgaWorkspaceSize: fb_layout.vga_workspace.end - fb_layout.vga_workspace.start,
+            pmuReservedSize: fb_layout.pmu_reserved_size,
             ..Zeroable::init_zeroed()
         });
 
-- 
2.53.0